Method of indirect heating using laser

ABSTRACT

An indirect heating method using a laser according to an aspect of the present disclosure includes: a first process of adjacently placing a first material structure containing a metal and a second material structure containing a mineral; and a second process of directly heating the first material structure to indirectly heat the second material structure adjacent to the first material structure by emitting a laser to the first material structure.

TECHNICAL FIELD

The present disclosure relates to a heating method using a laser and more particularly, to an indirect heating method using a laser.

BACKGROUND

Examples of heating methods include emitting a laser to a target object. A laser refers to condensed light obtained by concentrating energy spread in the space on one point. It is possible to concentrate tremendous energy by overlapping waves sharing the same point in the space. To operate a laser, a special medium, such as a special gas, crystal, or diode, that transmits a laser is needed. If energy in the form of electricity, radio wave, or light is injected into such a medium, electrons in the medium absorb the energy and then jump into the outer electron shells and thus atoms are in an excited state. If light is injected thereto, the excited atoms collide with photons to release numerous photons and return to a stable state, i.e., low-energy state. In this case, the released photons collide again with other atoms to release numerous photons. While this process is rapidly repeated, the photons are suddenly released into light.

One of the prior art technologies is disclosed in Korean Laid-open Publication No. 20150105195 (published on Sep. 16, 2015 and entitled “Laser heating treatment method and method for manufacturing solid state imaging device”).

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The present disclosure is conceived to provide a method of indirect heating of a mineral-containing material using a laser. However, this problem is provided for illustrative purposes only but not intended to limit the scope of the present disclosure.

Means for Solving the Problems

An aspect of the present disclosure provides an indirect heating method using a laser. The indirect heating method using a laser includes: a first process of adjacently placing a first material structure containing a metal and a second material structure containing a mineral; and a second process of directly heating the first material structure to indirectly heat the second material structure adjacent to the first material structure by emitting a YAG laser, a diode laser, or a CO₂ laser to the first material structure. The CO₂ laser is implemented using CO₂ as a source and may be a long-wavelength laser having a mean wavelength of 10 μm to 11 f. The YAG laser is implemented using neodymium-doped yttrium aluminum garnet (Nd:YAG) as a source and may have a wavelength of 532 nm, 940 nm, 1064 nm, 1120 nm, 1320 nm, or 1440 nm and may be doped with erbium (Er), ytterbium (Yb), or the like instead of neodymium (Nd).

In the indirect heating method using a laser, the first material structure and the second material structure may be placed in contact with each other.

In the indirect heating method using a laser, heat generated by emitting the laser to the first material structure may be more than heat generated by emitting the laser to the second material structure.

In the indirect heating method using a laser, the first process may include: forming an insulating film within a trench implemented in a device structure and forming, as the second material structure, a channel film of a second material on the insulating film within the trench; and after forming the channel film, forming, as the first material structure, a core portion of a first material filing an empty space within the trench and a laser receiving pad of the first material on a top surface of the device structure to be connected to the core portion, and the second process may include heating or melting the second material by emitting the laser onto the laser receiving pad to reduce a resistance of the channel film. In this case, the device structure may include a vertical NAND (VNAND) structure, and the second material may include polysilicon.

In the indirect heating method using a laser, the first process may include: forming a bottom electrode within a trench implemented in a device structure; forming, as the second material structure, a dielectric film of a second material on the bottom electrode within the trench; and forming, as the first material structure, a top electrode of a first material on the dielectric film within the trench and a laser receiving pad of the first material on a top surface of the device structure to be connected to the top electrode, and the second process may include heating or melting the second material by emitting the laser onto the laser receiving pad to increase a dielectric constant of the dielectric film. In this case, the device structure may include a capacitor structure of a DRAM, and the first material may include titanium nitride (TiN) or ruthenium (Ru) and the second material may include any one of HfO₂, HfSiO₄, ZrO₂, ZrSiO₄, La₂O₃, LaAlO₃, Al₂O₃, Ta₂O₅, Y₂O₃, TiO₂, and SrTiO₃. Further, the second process may include sequential phase transformations of the dielectric film into an amorphous structure, a monoclinic structure, a tetragonal structure, and a cubic structure.

In the indirect heating method using a laser, the first process may include: forming a gate oxide film to form a transistor structure of a memory device; forming, as the second material structure, a polysilicon film on the gate oxide film; and sequentially forming, as the first material structure, a titanium nitride (TiN) film, a tungsten nitride (WN) film, a tungsten silicide (WSi) film, or a tantalum nitride (TaN) film and a tungsten (W) film on the polysilicon film, and the second process may include heating or melting at least a part of the polysilicon film by emitting the laser onto the tungsten film to reduce an equivalent oxide thickness (EOT) of the transistor.

In the indirect heating method using a laser, the first process may include: forming, as the second material structure, a dielectric film to form a transistor structure of a logic device; and sequentially forming, as the first material structure, a titanium nitride (TiN) film and a tungsten (W) film on the polysilicon film, and the second process may include heating or melting at least a part of the polysilicon film by emitting the laser onto the tungsten film to reduce an equivalent oxide thickness (EOT) of the transistor.

In the indirect heating method using a laser, the first process may include: forming, as the second material structure, an amorphous polysilicon film; and forming the first material structure on the amorphous polysilicon film, and the second process may include heating or melting at least a part of the amorphous polysilicon film by emitting the laser onto the first material structure to reduce a resistance of the second material structure.

In the indirect heating method using a laser, the first process may include forming, as the second material structure, a photosensitive film on the first material structure, and the second process may include baking the photosensitive film by emitting the laser onto the first material structure.

Effects of the Invention

According to an embodiment of the present disclosure, it is possible to implement a method of indirect heating of a mineral-containing material using a YAG laser, a diode laser, or a CO₂ laser. The scope of the present disclosure is not limited by this effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flowchart illustrating an indirect heating method using a laser according to an embodiment of the present disclosure.

FIG. 2 to FIG. 4 illustrate a method of heating a channel film in a vertical NAND (VNAND) structure as an indirect heating method using a laser according to an embodiment of the present disclosure.

FIG. 5 illustrates a DRAM capacitor structure implemented by employing an indirect heating method using a laser according to an embodiment of the present disclosure.

FIG. 6 sequentially illustrates an EUV lithography process.

FIG. 7 illustrates a contact structure of a DRAM implemented by employing an indirect heating method using a laser according to an embodiment of the present disclosure.

FIG. 8 illustrates a S/D structure of a cell implemented by employing an indirect heating method using a laser according to an embodiment of the present disclosure.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereafter, embodiments of the present disclosure will be described in more detail with reference to the accompanying drawings. However, the present disclosure is not limited to the following embodiments, but may be implemented in various different forms. The embodiments are provided only to complete disclosure of the present disclosure and to fully provide a person with ordinary skill in the art with the category of the invention. Further, for convenience of explanation, the sizes of components may be exaggerated or reduced relative to one another in the drawings.

FIG. 1 is a flowchart illustrating an indirect heating method using a laser according to an embodiment of the present disclosure.

Referring to FIG. 1, an indirect heating method using a laser according to an embodiment of the present disclosure includes: a first process of adjacently placing a first material structure containing a metal and a second material structure containing a mineral (S100); and a second process of directly heating the first material structure to indirectly heat the second material structure adjacent to the first material structure by emitting a long-wavelength laser to the first material structure (S200). The materials may be so composed that heat generated by emitting the laser to the first material structure is more than heat generated by emitting the laser to the second material structure.

According to some embodiments of the present disclosure, the long-wavelength laser may be a CO₂ laser. That is, it is implemented using CO₂ as a source and may have a mean wavelength of 10 μm to 11 μm (e.g., 10.6 μm). The CO₂ laser can oscillate infrared light of 10.6 μm between vibrational levels of CO₂ gas molecules and has high efficiency and thus can easily output high power. For example, when a DC voltage of about 10 kV is applied to a pyrex tube having a length of about 1 m while CO₂, He, and N₂ are allowed to flow therein at a predetermined ratio, a glow discharge occurs. A population inversion will be described. A N₂ molecule is excited to a vibrational level of V″=1 from V″=0 due to a collision between an electron and N₂ during a discharge. This excited level is not much different in energy from (001) vibrational level of a CO₂ molecule, and a collision between the two molecules causes the N₂ molecule to transfer energy to the CO₂ molecule and then fall down. Due to this process, the CO₂ molecule is excited to (001) level. Between (001) vibrational level of the excited CO₂ and (100) vibrational level lower in energy than (001) vibrational level, a population inversion is formed. Thus, laser oscillation can occur. Therefore, although laser oscillation occurs in a CO₂ molecule, efficient excitation to (001) level can occur by adding N₂. Meanwhile, lower (001) level can be easily eliminated by mixing a He gas, and, thus, the population inversion can easily occur. Therefore, the efficiency can be increased.

The CO₂ laser having a wavelength of 10.6 μm is implemented by this mechanism and can efficiently heat a material containing a metal having relatively many free electrons to a very high temperature (e.g., 2000° C. to 3000° C.). However, it is relatively difficult for the CO₂ laser to heat a material containing a mineral (e.g., SiO₂, Si, Si₃N₄).

In the present disclosure using these characteristics, a first material structure containing a metal and a second material structure containing a mineral are placed adjacent to each other (e.g., placed in contact with each other) and then, the laser having a mean wavelength of 10 μm to 11 μm and using CO₂ as a source is emitted to the first material structure to directly heat the first material structure and thus indirectly heat the second material structure adjacent to the first material structure.

Accordingly, the second material structure containing a mineral can be heated by selectively emitting the laser only to the patterned first material structure, and, thus, only the second material structure can be locally heated rather than heating the entire device. This advantage makes it possible to control the characteristics of the second material structure, suppress thermal degradation of the device, and reduce time and cost for manufacturing.

Meanwhile, although the CO₂ laser is described as a laser emitted to the first material structure in FIG. 1, a YAG laser or a diode laser may also be emitted to the first material structure. The YAG laser is a solid state laser implemented by adding various rare elements such as neodymium (Nd), erbium (Er), ytterbium (Yb), or the like into a yttrium aluminum garnet (YAG) crystal.

The YAG laser is implemented by this mechanism and can efficiently heat a material containing a metal having relatively many free electrons to a very high temperature. However, it is relatively difficult for the YAG laser to heat a material containing a mineral (e.g., SiO₂, Si, Si₃N₄).

In the present disclosure using these characteristics, a first material structure containing a metal and a second material structure containing a mineral are placed adjacent to each other (e.g., placed in contact with each other) and then, the YAG laser is emitted to the first material structure to directly heat the first material structure and thus indirectly heat the second material structure adjacent to the first material structure.

Hereafter, specific embodiments of the above-described indirect heating method using a laser will be described to facilitate understanding of the technical concept of the present disclosure.

First Embodiment

FIG. 2 to FIG. 3 are cross-sectional views sequentially illustrating a method of heating a channel film in a vertical NAND (VNAND) structure as an indirect heating method using a laser according to an embodiment of the present disclosure. FIG. 4 is a plan view of the structure illustrated in FIG. 3 when viewed from another side.

Referring to FIG. 1 to FIG. 4, the first process (S100) may include: forming insulating films 12, 14, and 16 within a trench 10 implemented in a device structure and forming, as the second material structure, a channel film 19 of a second material on the insulating films 12, 14, and 16 within the trench 10; and after forming the channel film 19, forming, as the first material structure 20, a core portion 20 a of a first material filing an empty space 18 within the trench 10 and a laser receiving pad 20 b of the first material on a top surface of the device structure to be connected to the core portion 20 a. Further, the second process (S200) may include heating or melting the second material by emitting the laser onto the laser receiving pad 20 b to reduce a resistance of the channel film 19.

The device structure may include a vertical NAND (VNAND) structure, and the second material may include polysilicon. The insulating films 12, 14, and 16 may include a trap layer formed of silicon nitride, a blocking-oxide layer 16 formed of aluminum oxide, and a HQ oxide layer 14 formed of silicon oxide.

With a conventional laser, there was a limit to heating or melting the entire polysilicon (having a depth of 4 μm to 5 μm) which forms a channel layer of a vertical NAND (VNAND) structure. However, if the first material is used for gap-fill or macaroni-fill and then annealing is performed using the CO₂ laser, the first material can be heated and a channel layer formed of polysilicon as the second material in contact with the first material can be heated or melted. Thus, a resistance can be reduced and a current of the channel can be increased. Then, the first material provided thereafter for gap-fill or macaroni-fill is removed by an appropriate method. As the number of stacks of the vertical NAND (VNAND) structure increases, it becomes more important to increase a current by reducing a resistance of the channel film 19. In the present embodiment, this can be implemented by forming the above-described first material structure around the channel film 19 and then performing CO₂ laser annealing.

Meanwhile, it is not easy to directly emit the CO₂ laser to the core portion 20 a having a small cross-section area to indirectly heat the channel film 19. Therefore, it is effective to form the laser receiving pad 20 b having a relatively large cross-section area and connected to the core portion 20 a and then emit the CO₂ laser to the laser receiving pad 20 b.

Second Embodiment

Referring to FIG. 1, the first process (S100) may include: forming a bottom electrode within a trench implemented in a device structure; forming, as the second material structure, a dielectric film of a second material on the bottom electrode within the trench; and forming, as the first material structure, a top electrode of a first material on the dielectric film within the trench and a laser receiving pad of the first material on a top surface of the device structure to be connected to the top electrode, and the second process (S200) may include heating or melting the second material by emitting the laser onto the laser receiving pad to increase a dielectric constant of the dielectric film.

FIG. 5 illustrates a DRAM capacitor structure implemented by employing an indirect heating method using a laser according to an embodiment of the present disclosure.

The device structure may include a capacitor structure of a DRAM illustrated in FIG. 5, and the first material may include titanium nitride (TiN) or ruthenium (Ru) and the second material may include any one of HfO₂, HfSiO₄, ZrO₂, ZrSiO₄, La₂O₃, LaAlO₃, Al₂O₃, Ta₂O₅, Y₂O₃, TiO₂, and SrTiO₃. In this case, the second process (S200) may include sequential phase transformations of the dielectric film into an amorphous structure, a monoclinic structure, a tetragonal structure, and a cubic structure. Thus, it is possible to implement a dielectric film having sufficiently high permittivity.

That is, the use of the CO₂ laser makes it possible to obtain a tetragonal structure or cubic structure with assured high permittivity from any one of HfO₂, HfSiO₄, ZrO₂, ZrSiO₄, La₂O₃, LaAlO₃, Al₂O₃, Ta₂O₅, Y₂O₃, TiO₂, and SrTiO₃ whose phase is transformed at a relatively high temperature and thus to implement higher dielectric characteristics.

Third Embodiment

Referring to FIG. 1, the first process (S100) may include: forming a gate oxide film to form a transistor structure of a memory device; forming, as the second material structure, a polysilicon film on the gate oxide film; and sequentially forming, as the first material structure, a titanium nitride (TiN) film, a tungsten nitride (WN) film, a tungsten silicide (WSi) film, or a tantalum nitride (TaN) film and a tungsten (W) film on the polysilicon film, and the second process (S200) may include heating or melting at least a part of the polysilicon film by emitting the laser onto the tungsten film to reduce an equivalent oxide thickness (EOT) of the transistor.

That is, the transistor structure of a DRAM (or FLASH) is formed of gate oxide/polysilicon/metal (TiN/W). Since it is easy to heat the metal, activation of B or P can be enhanced by inducing local heating or melting of the polysilicon in contact with the metal, and, thus, it is possible to reduce polysilicon depletion and thus reduce the EOT. That is, activation can be performed sufficiently to remove polysilicon depletion in the metal gate for a short time at a high temperature by metal assisted heating.

Fourth Embodiment

Referring to FIG. 1, the first process (S100) may include: forming, as the second material structure, a dielectric film to form a transistor structure of a logic device; and sequentially forming, as the first material structure, a titanium nitride (TiN) film, a tantalum nitride (TaN) film, a tungsten nitride (WN) film, or a tungsten silicide (WSi) film and a tungsten (W) film on the polysilicon film, and the second process (S200) may include heating or melting at least a part of the polysilicon film by emitting the laser onto the tungsten film to reduce an equivalent oxide thickness (EOT) of the transistor. In the present embodiment, the polysilicon film may be substituted with a high-k film.

That is, the transistor structure of a logic device is formed of High-k/TiN (or TaN)/W, and, thus, it is possible to indirectly heat the high-k material by heating the metal and then obtain higher-k and reduce the EOT by phase transformation.

Fifth Embodiment

Referring to FIG. 1, the first process (S100) may include: forming, as the second material structure, an amorphous polysilicon film; and forming the first material structure on the amorphous polysilicon film, and the second process (S200) may include heating or melting at least a part of the amorphous polysilicon film by emitting the laser onto the first material structure to reduce a resistance of the second material structure.

One of the methods for reducing a resistance of polysilicon (or amorphous silicon) is a poly-melt method which is an easy method to increase general grain sizes. By connecting polysilicon (or amorphous silicon) to a metal and using a CO₂ laser, melting of the polysilicon (or amorphous silicon) can be implemented by heating of the metal.

Sixth Embodiment

Referring to FIG. 1, the first process (S100) may include forming, as the second material structure, a photosensitive film on the first material structure, and the second process (S200) may include baking the photosensitive film by emitting the laser onto the first material structure.

For example, an EUV photosensitive film can be baked by depositing a metal under the EUV photosensitive film. Since EUV has a wavelength of 13.5 nm, the EUV photosensitive film can be affected even in the visible light region. Therefore, a CO₂ laser having the longest wavelength can be most efficient.

FIG. 6 sequentially illustrates an EUV lithography process. In FIG. 6, a pre-bake process (process 3) and a post-exposure bake process (process 5) are relevant to a diffusion process of acid and base and include the above-described second process (S200) of baking the photosensitive film by emitting the laser onto the first material structure.

Various other embodiments are also possible.

FIG. 7 illustrates a contact structure of a DRAM implemented by employing an indirect heating method using a laser according to an embodiment of the present disclosure. Referring to FIG. 7, a resistance of a polysilicon contact plug increases in the presence of a void. However, if a metal layer is added and polysilicon is indirectly heated by the above-described indirect heating method using a laser according to an embodiment of the present disclosure, the void can be removed by re recrystallization and a contact resistance can be reduced.

FIG. 8 illustrates a S/D structure of a memory cell implemented by employing an indirect heating method using a laser according to an embodiment of the present disclosure. Referring to FIG. 8, it is important for a new memory structure having an embedded cell array transistor to reduce Rs/Rc values in ON state. This issue can be solved by the above-described indirect heating method using a laser.

The present disclosure has been described with reference to the embodiments illustrated in the drawings, but these embodiments are merely illustrative and it should be understood by a person with ordinary skill in the art that various modifications and equivalent embodiments can be made without departing from the scope of the present disclosure. Therefore, the true technical protective scope of the present disclosure must be determined based on the technical concept of the appended claims. 

We claim:
 1. An indirect heating method using a laser, comprising: a first process of adjacently placing a first material structure containing a metal and a second material structure containing a mineral; and a second process of directly heating the first material structure to indirectly heat the second material structure adjacent to the first material structure by emitting a YAG laser, a diode laser, or a CO₂ laser to the first material structure.
 2. The indirect heating method using a laser of claim 1, wherein the first material structure and the second material structure are placed in contact with each other.
 3. The indirect heating method using a laser of claim 1, wherein heat generated by emitting the laser to the first material structure is more than heat generated by emitting the laser to the second material structure.
 4. The indirect heating method using a laser of claim 1, wherein the first process includes: forming an insulating film within a trench implemented in a device structure and forming, as the second material structure, a channel film of a second material on the insulating film within the trench; and after forming the channel film, forming, as the first material structure, a core portion of a first material filing an empty space within the trench and a laser receiving pad of the first material on a top surface of the device structure to be connected to the core portion, and the second process includes heating or melting the second material by emitting the laser onto the laser receiving pad to reduce a resistance of the channel film.
 5. The indirect heating method using a laser of claim 4, wherein the device structure includes a vertical NAND (VNAND) structure, and the second material includes polysilicon.
 6. The indirect heating method using a laser of claim 1, wherein the first process includes: forming a bottom electrode within a trench implemented in a device structure; forming, as the second material structure, a dielectric film of a second material on the bottom electrode within the trench; and forming, as the first material structure, a top electrode of a first material on the dielectric film within the trench and a laser receiving pad of the first material on a top surface of the device structure to be connected to the top electrode, and the second process includes heating or melting the second material by emitting the laser onto the laser receiving pad to increase a dielectric constant of the dielectric film.
 7. The indirect heating method using a laser of claim 6, wherein the device structure includes a capacitor structure of a DRAM, and the first material includes titanium nitride (TiN) and the second material include any one of HfO₂, HfSiO₄, ZrO₂, ZrSiO₄, La₂O₃, LaAlO₃, Al₂O₃, Ta₂O₅, Y₂O₃, TiO₂, and SrTiO₃.
 8. The indirect heating method using a laser of claim 7, wherein the second process includes sequential phase transformations of the dielectric film into an amorphous structure, a monoclinic structure, a tetragonal structure, and a cubic structure.
 9. The indirect heating method using a laser of claim 1, wherein the first process includes: forming a gate oxide film to form a transistor structure of a memory device; forming, as the second material structure, a polysilicon film on the gate oxide film; and sequentially forming, as the first material structure, a titanium nitride (TiN) film, a tungsten nitride (WN) film, a tungsten silicide (WSi) film, or a tantalum nitride (TaN) film and a tungsten (W) film on the polysilicon film, and the second process includes heating or melting at least a part of the polysilicon film by emitting the laser onto the tungsten film to reduce an equivalent oxide thickness (EOT) of the transistor.
 10. The indirect heating method using a laser of claim 1, wherein the first process includes: forming, as the second material structure, a dielectric film to form a transistor structure of a logic device; and sequentially forming, as the first material structure, a titanium nitride (TiN) film and a tungsten (W) film on the polysilicon film, and the second process includes heating or melting at least a part of the polysilicon film by emitting the laser onto the tungsten film to reduce an equivalent oxide thickness (EOT) of the transistor.
 11. The indirect heating method using a laser of claim 1, wherein the first process includes: forming, as the second material structure, an amorphous polysilicon film; and forming the first material structure on the amorphous polysilicon film, and the second process includes heating or melting at least a part of the amorphous polysilicon film by emitting the laser onto the first material structure to reduce a resistance of the second material structure.
 12. The indirect heating method using a laser of claim 1, wherein the first process includes forming, as the second material structure, a photosensitive film on the first material structure, and the second process includes baking the photosensitive film by emitting the laser onto the first material structure. 